Jaegers molt at sea, and these poorly known molts result in variable and confusing fall and winter plumages. We summarize the progression of molts and appearance of the plumages in 11 Long-tailed Jaegers (Stercorarius longicaudus), of four age groups, photographed off Chile in December 1993. The central rectrices in these birds were short, blunt-tipped, and either plain brown or boldly barred black and white, indicating that, in at least some individuals, these feathers were replaced for a second time within the molt cycle. The body plumage of five adults was quite different from the breeding plumage and differed from nonbreeding plumages depicted in the literature. Individuals replacing primaries during the second prebasic molt showed worn and bleached head and body feathers, indicating only limited feather replacement since the preformative molt rather than a complete body molt in their second fall as widely reported. Examination of 647 specimens confirmed that in jaegers body-feather molt is partial to incomplete in fall and usually complete in spring. Using the Humphrey–Parkes nomenclature, we thus propose a novel molt and plumage terminology for jaegers, in which birds breed in basic plumage and undergo a partial prealternate body molt in fall. Under this interpretation, a limited first prealternate body-feather molt occurs during the second summer and fall, and the first cycle is completed at an age of 15–18 months. The later and complete preformative molt, from November to March, produces stronger formative feathers, allowing the second prebasic body molt to be “pushed back” by 6 months, leading to a spring-to-spring cycle of prebasic molt. We suggest that a prealternate body-feather molt has evolved in jaegers to provide protective coloration for flight-feather molt, as has been proposed for ducks and ptarmigan, or perhaps for social signaling or just to replace feathers that wear quickly because of intense annual solar exposure.